Digital Subscriber Line (xDSL) is a high-speed data transmission technology, and occupies high band. Crosstalk is increasingly noticeable in the xDSL, and Far End Crosstalk (FEXT) affects transmission performance of the line drastically. As shown in FIG. 1, when multiple lines in a bundle of cables need to activate the xDSL service, there will be crosstalk, and the FEXT makes some lines suffer a low rate, unstable performance, and even failure of service activation, which ends in a low line activation rate of the Digital Subscriber Line Access Multiplexer (DSLAM).
In the prior art, the primary means of canceling the FEXT is signal processing, which stabilizes the line performance. As shown in FIG. 2, in the uplink transmission direction (namely, the signal is transmitted from the Customer Premises Equipment (CPE) to the central office), the data transmitted from the CPE passes through the channel H, and then a noise vector n is overlaid to the data. The data y received at the central office undergoes joint crosstalk cancelation performed by a filtering canceller W to ensure that the user data received at the CPE is free from crosstalk. The signal finally acquired by the central office is {tilde over (y)}=WHx+Wn. When WH is a diagonal matrix, the crosstalk is eliminated. As shown in FIG. 3, in the downlink transmission direction (namely, the signal is transmitted from the central office or far end to the CPE), a precoder P at the CPE preprocesses the data x to be transmitted, the preprocessed data passes through the channel H, and then a noise vector n is overlaid to the data. The data received at the central office or far end is free from crosstalk. Therefore, the signal finally acquired by the CPE is {tilde over (y)}=HPx+n. When HP is a diagonal matrix, the crosstalk is eliminated. The above channel H is an M×M channel transmission matrix, and n is an M×1 noise vector.
In a practical implementation scheme, the central office or far end trains and updates the coefficient of the precoder according to data transmission errors fed back by the CPE to make the HP be a diagonal matrix. The formula for updating the coefficient is Pk=Pk+u*Ek*XkH, where P is the precoding coefficient of the subcarrier numbered k (namely, subcarrier k), u is the update step length, and Ek=Yk−Xk represents the data transmission error of subcarrier k. Also, the central office trains and updates the coefficient of the canceller according to the data transmission errors to make WH be a diagonal matrix.
In the software and hardware implementation of the precoder and the canceller, the precoding and the cancellation are based on each subcarrier separately. That is, the filtering is performed after the filtering coefficient of each subcarrier is acquired according to the data transmission errors. Generally, there are many subcarriers need to subject to crosstalk cancelation, which involves very large amount of operation, consumes hardware resources and operation time drastically, and increases the cost.